Burkhardt Dwight A, Fahey Patrick K, Sikora Michael A
Department of Psychology, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Vis Neurosci. 2007 Nov-Dec;24(6):765-74. doi: 10.1017/S0952523807070630.
The temporal dynamics of the response of neurons in the outer retina were investigated by intracellular recording from cones, bipolar, and horizontal cells in the intact, light-adapted retina of the tiger salamander (Ambystoma tigrinum), with special emphasis on comparing the two major classes of bipolars cells, the ON depolarizing bipolars (Bd) and the OFF hyperpolarizing bipolars (Bh). Transfer functions were computed from impulse responses evoked by a brief light flash on a steady background of 20 cd/m(2). Phase delays ranged from about 89 ms for cones to 170 ms for Bd cells, yielding delays relative to that of cones of about 49 ms for Bh cells and 81 ms for Bd cells. The difference between Bd and Bh cells, which may be due to a delay introduced by the second messenger G-protein pathway unique to Bd cells, was further quantified by latency measurements and responses to white noise. The amplitude transfer functions of the outer retinal neurons varied with light adaptation in qualitative agreement with results for other vertebrates and human vision. The transfer functions at 20 cd/m(2) were predominantly low pass with 10-fold attenuation at about 13, 14, 9.1, and 7.7 Hz for cones, horizontal, Bh, and Bd cells, respectively. The transfer function from the cone voltage to the bipolar voltage response, as computed from the above measurements, was low pass and approximated by a cascade of three low pass RC filters ("leaky integrators"). These results for cone-->bipolar transmission are surprisingly similar to recent results for rod-->bipolar transmission in salamander slice preparations. These and other findings suggest that the rate of vesicle replenishment rather than the rate of release may be a common factor shaping synaptic signal transmission from rods and cones to bipolar cells.
通过对虎螈（钝口螈）完整、光适应视网膜中的视锥细胞、双极细胞和水平细胞进行细胞内记录，研究了外视网膜神经元反应的时间动态，特别着重比较了两类主要的双极细胞，即ON去极化双极细胞（Bd）和OFF超极化双极细胞（Bh）。传递函数是根据在20 cd/m²的稳定背景上短暂闪光诱发的冲动反应计算得出的。相位延迟范围从视锥细胞的约89毫秒到Bd细胞的170毫秒，Bh细胞相对于视锥细胞的延迟约为49毫秒，Bd细胞为81毫秒。Bd细胞和Bh细胞之间的差异可能归因于Bd细胞特有的第二信使G蛋白途径引入的延迟，通过潜伏期测量和对白噪声的反应进一步进行了量化。外视网膜神经元的幅度传递函数随光适应而变化，在定性上与其他脊椎动物和人类视觉的结果一致。在20 cd/m²时，视锥细胞、水平细胞、Bh细胞和Bd细胞的传递函数主要为低通，在约13、14、9.1和7.7赫兹处分别有10倍的衰减。根据上述测量计算得出的从视锥细胞电压到双极细胞电压反应的传递函数为低通，并由三个低通RC滤波器（“泄漏积分器”）级联近似。视锥细胞到双极细胞传递的这些结果与最近在蝾螈切片制备中杆细胞到双极细胞传递的结果惊人地相似。这些以及其他发现表明，囊泡补充速率而非释放速率可能是塑造从视杆细胞和视锥细胞到双极细胞突触信号传递的共同因素。
